Apparatus for aligning the wheels of an automobile, truck or trailer suspension system and, in particular, apparatus for aligning the rolling plane of each of the wheels to the thrust line of the rear wheels and/or the geometric center-line of the suspension and as per manufacturer's specifications.
With the scaling down in the size of conventional automobiles, automobile design engineers have changed the suspension system of the typical automobile from the heretofore conventional solid frame construction to a unibody construction and/or some variation thereof, where the front suspension is no longer directly coupled to the rear suspension. Thus, one now encounters independent front and rear suspensions as well as vehicles where each wheel is independently suspended from the others. Due to the redesigning of the suspension systems, however, problems have arisen in ensuring the maintenance of the proper alignment of each of a vehicle's four wheels over time and which problems are not easily cured with available alignment apparatus.
When heretofore one could assume that a vehicle's frame was relatively constant and straight so as to permit a line of sight type adjustment between the front and rear suspensions, this condition no longer holds true. Due to the independent nature of the front and rear suspensions, their respective mountings relative to the vehicle and each other may now vary by design, just as the alignment of each wheel's suspension may become skewed from road hazards. In particular, with unibody construction and the joining of each wheel's suspension to the sheet metal structure of a vehicle, a variety of stresses are now placed on each wheel and the vehicle body that may induce wheel misalignment. Further, misalignment may occur during manufacture, such as where one wheel is set forward or back of the adjacent wheel so as to result in a setback or skewing of one side of the otherwise rectangular suspension. The assumptions of heretofore conventional alignment techniques thus no longer hold true and to employ them quite often results in a vehicle with improper handling characteristics and excessive tire wear, even though it is thought to be properly aligned.
Proper vehicle alignment permits the vehicle to roll in a straight line, with the steering wheel centered. This condition is achieved with the present invention via the aligning of the wheels to the vehicle thrust line and which has been defined as the line bisecting the total rear wheel toe angle or the line perpendicular to the average axes of the two rear wheels.
With the independent mounting of each of the wheels or at least the front and rear wheel suspension pairs, the above alignment condition is achieved by ensuring that each wheel is aligned relative to the others so that the "rolling plane" or imaginary vertical plane through each wheel as it rotates relative to the ground is parallel to the vehicle thrust line and within factory specifications. This end is particularly achieved by first determining the thrust line of the wheels of the rear suspension portion and correcting them to be within factory specifications. Thereafter, the condition of the wheels of the front suspension portion is determined and corrected to be within factory specifications and at the same thrust angle as the rear wheels. Assuming, therefore, that the steering wheel was held in a centered position during these corrections, an operator can be assured that afterwards the rolling plane of each of the wheels will be aligned to specifications and be parallel to the vehicle thrust line.
In order to independently align the four wheels of a conventional automobile, it first becomes necessary to establish a reference of some sort and relative to which reference, each of the wheels may be adjusted. Previously, this reference was the center line of the frame suspension. The present invention, however, achieves its reference by establishing an adjustable rectangular frame or "halo" about a vehicle so as to concentrically circumscribe each of the tires and relative to which halo the geometric center line of the suspension (and which is to be distinguished from the geometric center line of the frame) is determined and the wheels are aligned.
It is accordingly necessary to center the vehicle relative to the halo and which is centered in a concentric, equidistant fashion in one embodiment of the present invention via individual guide pins that are mounted relative to each wheel's hub and via measuring tapes mounted to the halo. Thereafter, individual rolling plane gauge assemblies are coupled to each wheel via respective adjustable three point connecting assemblies that are suitably adjusted to remove all wheel run-out before taking wheel measurements. Thereafter, a toe angle indicating bar is magnetically coupled to the rolling plane gauge along with a magnetic caster/camber detecting gauge. Upon coupling each rolling plane gauge to each wheel, toe condition is directly indicated on individual scales mounted to the halo fore and aft of each wheel. Upon further detecting and correcting the individual toe and camber condition at each rear wheel, the opposite wheels or front wheels are adjusted relative to the rolling plane established for each rear wheel. At the same time, the toe, caster and camber conditions and king-pin inclination or strut angle are measured and corrected as necessary to bring them within factory specifications. Thus, the rolling plane of each wheel is adjusted to be within factory specifications and at the same thrust angle relative to the geometric center line of the vehicle's suspension system.
The present invention thus permits the relative alignment of a vehicle's four wheels in an economical fashion and does not require the use of microprocessor controllers, optical alignment devices or specially designed vehicle support racks, such as are required with more elaborate and costly systems like those manufactured by Hunter Engineering Co., Bridgeton, Mo. Instead, it produces similar results with a less costly assembly that may be used with any of a variety of exiting support racks.
The above objects, advantages and distinctions of the present invention as well as various others will, however, become more apparent upon reference to the following description thereof with respect to the appended drawings. Before referring thereto, though, it is to be recognized that while the present invention is described with respect to three presently preferred embodiments, various modifications may be made thereto by those of skill in the art without departing from the spirit and scope thereof.